diff --git a/src/saveload/extended_ver_sl.h b/src/saveload/extended_ver_sl.h
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+++ b/src/saveload/extended_ver_sl.h
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+/* $Id$ */
+
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see .
+ */
+
+/** @file extended_ver_sl.h Functions/types related to handling save/load extended version info. */
+
+#ifndef EXTENDED_VER_SL_H
+#define EXTENDED_VER_SL_H
+
+#include "../core/bitmath_func.hpp"
+
+#include
+
+enum SaveLoadVersion : uint16;
+
+/**
+ * List of extended features, each feature has its own (16 bit) version
+ */
+enum SlXvFeatureIndex {
+ XSLFI_NULL = 0, ///< Unused value, to indicate that no extended feature test is in use
+ //===================================
+ // COMMON EXTENDED FEATURES
+ //===================================
+ XSLFI_VERSION_LABEL, ///< Version label
+ XSLFI_PATCHPACK_MAJOR_VERSION, ///< Patchpack major version
+ //===================================
+ // PATCHPACK 5.X FEATURES
+ //===================================
+ XSLFI_DAYLENGTH, ///< Variable day length
+ XSLFI_STATION_NEWGRF, ///< Station names based on industries
+ XSLFI_INFRASTRUCTURE, ///< Custom infrastructure base costs
+ XSLFI_RUNNING_COST_MULT, ///< Running cost multiplier
+ XSLFI_PLANE_RANGE_MULT, ///< Plane range multiplier
+ XSLFI_EXTRA_EXPENSES, ///< Additional expense types in the expenses window
+ XSLFI_IMPROVED_BREAKDOWNS, ///< Improved breakdowns patch
+ XSLFI_BREAKDOWN_SCALER, ///< Additional breakdown chance scaler
+ XSLFI_TOWN_IMPROVEMENTS, ///< Configurable bribe risk and town growth factor
+ XSLFI_DILAPIDATION, ///< Station dilapidation
+ //===================================
+ XSLFI_SIZE, ///< Total count of features, including null feature
+};
+
+extern uint16 _sl_xv_feature_versions[XSLFI_SIZE];
+
+/**
+ * Operator to use when combining traditional savegame number test with an extended feature version test
+ */
+enum SlXvFeatureTestOperator {
+ XSLFTO_OR = 0, ///< Test if traditional savegame version is in bounds OR extended feature is in version bounds
+ XSLFTO_AND ///< Test if traditional savegame version is in bounds AND extended feature is in version bounds
+};
+
+/**
+ * Structure to describe an extended feature version test, and how it combines with a traditional savegame version test
+ */
+struct SlXvFeatureTest {
+ using TestFunctorPtr = bool (*)(uint16, bool); ///< Return true if feature present, first parameter is standard savegame version, second is whether standard savegame version is within bounds
+
+ private:
+ uint16 min_version;
+ uint16 max_version;
+ SlXvFeatureIndex feature;
+ SlXvFeatureTestOperator op;
+ TestFunctorPtr functor = nullptr;
+
+ public:
+ SlXvFeatureTest()
+ : min_version(0), max_version(0), feature(XSLFI_NULL), op(XSLFTO_OR) { }
+
+ SlXvFeatureTest(SlXvFeatureTestOperator op_, SlXvFeatureIndex feature_, uint16 min_version_ = 1, uint16 max_version_ = 0xFFFF)
+ : min_version(min_version_), max_version(max_version_), feature(feature_), op(op_) { }
+
+ SlXvFeatureTest(TestFunctorPtr functor_)
+ : min_version(0), max_version(0), feature(XSLFI_NULL), op(XSLFTO_OR), functor(functor_) { }
+
+ bool IsFeaturePresent(SaveLoadVersion savegame_version, SaveLoadVersion savegame_version_from, SaveLoadVersion savegame_version_to) const;
+};
+
+bool SlXvIsFeaturePresent(SlXvFeatureIndex feature, uint16 min_version = 1, uint16 max_version = 0xFFFF);
+
+/**
+ * Returns true if @p feature is missing (i.e. has a version of 0)
+ */
+inline bool SlXvIsFeatureMissing(SlXvFeatureIndex feature)
+{
+ return !SlXvIsFeaturePresent(feature);
+}
+
+const char *SlXvGetFeatureName(SlXvFeatureIndex feature);
+
+/**
+ * sub chunk flags, this is saved as-is
+ * (XSCF_EXTRA_DATA_PRESENT and XSCF_CHUNK_ID_LIST_PRESENT must only be set by the save code, and read by the load code)
+ */
+enum SlxiSubChunkFlags {
+ XSCF_NULL = 0, ///< zero value
+ XSCF_IGNORABLE_UNKNOWN = 1 << 0, ///< the loader is free to ignore this without aborting the load if it doesn't know what it is at all
+ XSCF_IGNORABLE_VERSION = 1 << 1, ///< the loader is free to ignore this without aborting the load if the version is greater than the maximum that can be loaded
+ XSCF_EXTRA_DATA_PRESENT = 1 << 2, ///< extra data field is present, extra data in some sub-chunk/feature specific format, not used for anything yet
+ XSCF_CHUNK_ID_LIST_PRESENT = 1 << 3, ///< chunk ID list field is present, list of chunks which this sub-chunk/feature adds to the save game, this can be used to discard the chunks if the feature is unknown
+
+ XSCF_IGNORABLE_ALL = XSCF_IGNORABLE_UNKNOWN | XSCF_IGNORABLE_VERSION, ///< all "ignorable" flags
+};
+DECLARE_ENUM_AS_BIT_SET(SlxiSubChunkFlags)
+
+struct SlxiSubChunkInfo;
+
+typedef uint32 SlxiSubChunkSaveProc(const SlxiSubChunkInfo *info, bool dry_run); ///< sub chunk save procedure type, must return length and write no data when dry_run is true
+typedef void SlxiSubChunkLoadProc(const SlxiSubChunkInfo *info, uint32 length); ///< sub chunk load procedure, must consume length bytes
+
+/** Handlers and description of chunk. */
+struct SlxiSubChunkInfo {
+ SlXvFeatureIndex index; ///< feature index, this is saved
+ SlxiSubChunkFlags flags; ///< flags, this is saved
+ uint16 save_version; ///< version to save
+ uint16 max_version; ///< maximum version to accept on load
+ const char *name; ///< feature name, this *IS* saved, so must be globally unique
+ SlxiSubChunkSaveProc *save_proc; ///< save procedure of the sub chunk, this may be nullptr in which case no extra chunk data is saved
+ SlxiSubChunkLoadProc *load_proc; ///< load procedure of the sub chunk, this may be nullptr in which case the extra chunk data must be missing or of 0 length
+ const char *chunk_list; ///< this is a list of chunks that this feature uses, which should be written to the savegame, this must be a comma-seperated list of 4-character IDs, with no spaces, or nullptr
+};
+
+void SlXvResetState();
+
+void SlXvSetCurrentState();
+
+void SlXvCheckSpecialSavegameVersionsA();
+
+void SlXvCheckSpecialSavegameVersionsB();
+
+bool SlXvIsChunkDiscardable(uint32 id);
+
+#endif /* EXTENDED_VER_SL_H */